Biomedical optical devices are increasingly being used to quantitatively analyze the optical properties of living tissue. In one application domain, devices are being used to produce tomographic images of the bulk optical properties of large tissue structures. As with other imaging technologies, their practical use requires the availability of a calibration mediums (i.e., phantoms) that serve to calibrate and quantify system performance.
Because of the recent introduction of systems capable of generating an image time-series, a need has arisen for phantoms whose optical properties can be suitably varied in ways that mimic the temporal variations of tissue optical properties, such as those produced by changes in vascular reactivity or oxidative demand that result in optical changes that are wavelength-dependent., for example.
One approach that has been reported as a means to measure dynamic states (time-varying states) is the use of elastomeric materials containing chromagens of interest. The internal volume or concentration of chromagen is varied in time (Schmitz et al., Applied Optics, 39, 6466-6486, 2000). For example, latex balloons are filled with a dilute hemoglobin solution and attached to a piston pump that serves to vary its internal volume. Detection of transmitted or reflected light having passed through a scattering medium containing such inclusions produces a time-varying optical signal. In principle this approach can be extended to include multiple inclusions, each controlled separately and differing in the concentration or composition of a chromagen. In situations wherein it is desirable to mimic complex dynamic states of tissue, a system of this sort invariably requires use of complex fluidic control devices. More desirable would be to employ materials or devices with optical properties that can be electrically modulated.
One well-known device class having this property is acoustic-optical cells. These devices however, employ bulky support mechanics that can attenuate the incident optical field. These devices and also require an incident acoustic field.